Coatings, method of manufacture, and the articles derived therefrom

ABSTRACT

A turbine component comprises a substrate; and a crystalline coating disposed on a surface of the substrate, wherein the crystalline coating comprises tin and yttrium in an amount greater than or equal to about 0.05 atomic percent based upon the total coating. A method of making a turbine component comprises disposing a coating composition on a substrate, wherein the coating composition comprises tin and yttrium in an amount greater than or equal to about 0.1 atomic percent based upon the total coating composition. A crystalline coating comprises tin and yttrium in an amount greater than or equal to about 0.05 atomic percent based upon the total coating.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

The United States Government may have certain rights in this inventionpursuant to Contract No. F33615-98-C-5215, awarded by the United StatesAir Force, United States Department of Defense.

BACKGROUND OF INVENTION

This disclosure generally relates to turbine systems, and moreparticularly to environmentally resistant coatings for the variouscomponents employed in such turbine systems.

Turbines are devices that generate rotary mechanical power from theenergy in a stream of moving fluid, and may be used in aircraft,watercraft (both marine and fresh water), various types of landcraft,and the like. Materials from which turbine components may be fabricatedtypically include those from a class of materials known as superalloys,particularly superalloys in which the base constituent is an alloy ofnickel (Ni), iron (Fe), or cobalt (Co). Despite their generally superiorchemical and physical properties, temperature constraints, particularlyfor single-crystal nickel-based superalloys, can limit the use of suchsuperalloys in turbine engines in which extreme temperature conditionsmay be experienced.

In order to overcome some of the temperature limitations of thesesuperalloys, newer materials based on niobium (Nb) and molybdenum havebeen developed. The niobium based materials used in turbine applicationsare termed niobium based refractory metallic-intermetallic composites(hereinafter Nb based RMICs), while those based on molybdenum are termedmolybdenum-silicide based composites. Both Nb based RMICs andmolybdenum-silicide based composites have melting temperatures greaterthan 1700° C., which exceeds the current temperature service limit ofnickel based superalloys.

Although the Nb based RMICs and molybdenum-silicide based compositesdisplay high melting temperatures, they can undergo rapid oxidation attemperatures of about 1090° C. to about 1370° C. In addition, anothertype of oxidation, generally termed as ‘pesting’, occurs at intermediatetemperatures of about 760° C. to about 990° C. Pesting is a phenomenonthat is characterized by the disintegration of a material into pieces orpowders after exposure to air at intermediate temperatures. Refractorymetals, particularly molybdenum, exhibit poor resistance to pestingoxidation. It is therefore desirable to be able to manufacture turbinecomponents that are capable of withstanding service temperatures ofgreater than or equal to about 1000° C., that have an increasedresistance to oxidation at temperatures of about 1090° C. to about 1370°C., and that have an increased resistance to pesting at temperatures ofabout 760° C. to about 980° C.

SUMMARY OF INVENTION

A turbine component comprises a substrate; and a crystalline coatingdisposed on a surface of the substrate, wherein the crystalline coatingcomprises tin and yttrium in an amount greater than or equal to about0.05 atomic percent based upon the total coating.

In one embodiment, a method of making a turbine component comprisesdisposing a coating composition on a substrate, wherein the coatingcomposition comprises tin and yttrium in an amount greater than or equalto about 0.1 atomic percent based upon the total coating composition.

In another embodiment, a crystalline coating comprises tin and yttriumin an amount greater than or equal to about 0.05 atomic percent basedupon the total coating.

The above described and other features are exemplified by the followingfigures and the detailed description.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic representation of a cross-sectional view of aturbine system;

FIG. 2 is a schematic cross-sectional view of an environmentallyresistant coating deposited on a niobium based refractory metalintermetallic composite or a molybdenum-silicide based compositesubstrate;

FIG. 3 is a schematic cross-sectional view of a thermal barrier coatingand an environmentally resistant coating deposited on a niobium basedrefractory metal intermetallic composite or a molybdenum-silicide basedcomposite substrate;

FIG. 4 is a graphical representation of a phase diagram for an Nb—Al—Crternary system;

FIG. 5 is a graphical representation of oxide penetration measurementsfor Samples 1-5 at different conditions of temperature and time;

FIG. 6 is a graphical representation of the reduction in diameter forSamples 1-5 at different conditions of temperature and time;

FIG. 7 depicts photomicrographs showing oxidation penetration of Samples2, 4 and 5;

FIG. 8 is a graphical representation of oxide penetration measurementsfor Samples 6-8 at different conditions of temperature and time; and

FIG. 9 depicts photomicrographs showing oxidation penetration of Samples7 and 8.

DETAILED DESCRIPTION

Disclosed herein is a crystalline, environmentally resistant coatingcomposition comprising tin and yttrium, wherein the total amount of tinand yttrium is greater than or equal to about 0.1 atomic percent basedupon the total coating composition. The novel coating composition can beapplied to Nb based RMICs and molybdenum-silicide based composites usedas turbine components to form a coating that improves resistance tooxidation at temperatures of about 1090° C. to about 1370° C. Thesecoatings also provide Nb based RMICs and molybdenum-silicide basedcomposites with an increased resistance to pesting at temperatures ofabout 760° C. to about 980° C. Also disclosed herein is a method fordepositing the above coating on turbine components.

In the following detailed description, like reference charactersdesignate like or corresponding parts throughout the several views shownin the figures. Furthermore, it is also understood that theillustrations are for the purpose of describing various embodiments andare not intended to be construed as being limiting in any manner.

Referring to the drawings in general and to FIG. 1 in particular, aschematic diagram of a turbine system 10 is shown. Turbine system 10 maybe utilized in various applications such as aircraft, watercraft (e.g.,marine and fresh water such as those that operate on rivers, lakes, andthe like), landcraft, land based power generation units, and the like.The turbine system 10 comprises a number of turbine components 11 thatare subject to temperatures of greater than or equal to about 1150° C.during normal operation. These turbine components 11 include, but arenot limited to: rotating blades 12, non-rotating vanes 16, shrouds 18,nozzles 20, combustors 24, and the like. Such turbine components 11 maybe formed from Nb based RMICs or from molybdenum-silicide basedcomposites and have service temperatures that are either comparable toor exceed the service temperatures of similar components formed from thenickel-based superalloys that are presently utilized.

In one exemplary embodiment, the Nb based RMICs that may be used to formthe turbine components 11 of the turbine system 10 may comprisetitanium, hafnium, silicon, chromium, and niobium. The Nb based RMICspreferably comprise about 19 to about 24 atomic percent titanium (Ti),about 1 to about 5 atomic percent hafnium (Hf), about 11 to about 22atomic percent silicon (Si), about 5 to about 14 atomic percent chromium(Cr), and a balance of niobium (Nb), based on the total composition ofthe Nb based RMICs. More preferably, the Nb based RMICs comprise about19 to about 24 atomic percent titanium, about 1 to about 5 atomicpercent hafnium, up to about 7 atomic percent tantalum (Ta), about 11 toabout 22 atomic percent silicon, up to about 6 atomic percent germanium(Ge), up to about 12 atomic percent boron (B), about 5 to about 14atomic percent chromium, up to about 4 atomic percent iron (Fe), up toabout 4 atomic percent aluminum (Al), up to about 3 atomic percent tin(Sn), up to about 3 atomic percent tungsten (W), up to about 3 atomicpercent molybdenum (Mo), and a balance of niobium, based on the totalcomposition of the Nb based RMICs. Most preferably, silicon, germanium,and boron together comprise about 11 to about 25 atomic percent of theNb based RMIC, iron and chromium together comprise about 5 to about 18atomic percent of the Nb based RMIC, and the ratio of the sum of atomicpercentages of niobium and tantalum present in the Nb based RMIC to thesum of atomic percentages of titanium and hafnium in the Nb based RMICis about 1.4 to about 2.2, i.e., 1.4<(Nb+Ta):(Ti+Hf)<2.2.

In another exemplary embodiment, the molybdenum-silicide based compositethat may be used to form the turbine components 11 of the turbine system10 comprises at least 10 volume percent of at least onemolybdenum-silicide and further comprises boron, chromium or acombination of boron and chromium. Molybdenum-silicides include, but arenot limited to, MoSi₂, Mo₃Si, Mo₅Si₃, and Mo₅SiB₂. Themolybdenum-silicide based composite preferably comprises about 2.5 toabout 13.5 atomic percent silicon, about 3.5 to about 26.5 atomicpercent boron, and a balance of molybdenum based on the totalcomposition of the molybdenum-silicide based composite. In yet anotherexemplary embodiment, the molybdenum-silicide based composite maycomprise about 13 to about 16 atomic percent silicon, about 25 to about40 atomic percent chromium, and a balance of molybdenum based on thetotal composition of the molybdenum-silicide based composite. Themolybdenum-silicide based composite may also include other elements, forexample, tantalum, titanium, zirconium, rhenium, carbon, hafnium,germanium, tungsten, vanadium, tin, and aluminum.

The turbine components 11 may be formed by a variety of differentprocesses such as, but not limited to, powder metallurgy processes(e.g., sintering, hot pressing, hot isostatic processing, hot vacuumcompaction, and the like), ingot casting followed by directionalsolidification, ingot casting followed by thermo-mechanical treatment,near-net-shape casting, chemical vapor deposition, physical vapordeposition, and the like. As stated above, in order to prevent theturbine components 11 from degradation due to oxidation and pesting, anenvironmentally resistant coating 34 may be disposed at a surface 33 ofa substrate 32 to form a coated article 30, such as a coated turbinecomponent, as is shown in FIG. 2.

It is generally desirable that the environmentally resistant coating 34is crystalline and comprises tin and yttrium (Y) in amounts of greaterthan or equal to about 0.05 atomic percent, and preferably furthercomprises chromium and aluminum. In one embodiment, the environmentallyresistant coating 34 comprises about 10 to about 67 atomic percentchromium, up to about 25 atomic percent silicon, about 5 to about 55atomic percent aluminum, about 15 to about 45 atomic percent of acombination of niobium and titanium, and an amount of greater than orequal to about 0.05 atomic percent of a combination of tin and yttriumbased on the total coating. The environmentally resistant coating 34 mayoptionally contain up to 20 atomic percent of germanium and up to about20 atomic percent of iron if desired. Preferably, the environmentallyresistant coating 34 is crystalline and comprises up to about 15 atomicpercent silicon, about 15 to about 52 atomic percent chromium, about 30to about 50 atomic percent aluminum, about 10 to about 25 atomic percentniobium, about 5 to about 20 atomic percent titanium, up to about 15atomic percent germanium, up to about 8 atomic percent iron, and anamount of greater than or equal to about 0.05 atomic percent of acombination of tin and yttrium based on the total coating.

In another embodiment the environmentally resistant coating 34 iscrystalline and comprises about 25 to about 60 atomic percent chromium,up to about 20 atomic percent aluminum, about 2 to about 40 atomicpercent niobium, about 5 to about 67 atomic percent silicon, about 2 toabout 40 atomic percent titanium, up to about 20 atomic percentgermanium, up to about 10 atomic percent iron, and an amount of greaterthan or equal to about 0.05 atomic percent of a combination of tin andyttrium, based on the total coating. Preferably the environmentallyresistant coating 34 comprises about 40 to about 60 atomic percentchromium, up to about 20 atomic percent aluminum, about 20 to about 25atomic percent niobium, about 10 to about 20 atomic percent silicon,about 8 to about 10 atomic percent titanium, up to about 10 atomicpercent iron, and an amount of greater than or equal to about 0.05atomic percent of a combination of tin and yttrium based on the totalcoating. Also preferably the environmentally resistant coating 34 iscrystalline and comprises about 25 to about 40 atomic percent chromium,up to about 4 atomic percent aluminum, about 5 to about 15 atomicpercent niobium, about 49 to about 64 atomic percent silicon, about 5 toabout 10 atomic percent titanium, up to about 4 atomic percent iron, andan amount of greater than or equal to about 0.05 atomic percent of acombination of tin and yttrium based on the total coating.

The environmentally resistant coating 34 may be applied to a substrate32 by one of or a combination of deposition techniques. A preferredtechnique is to coat the substrate 32 with a slurry comprising thecoating composition. The coating composition may be applied by dippingthe substrate 32 into the slurry, or by painting or spray painting thesubstrate 32 with the slurry. The coating composition comprises tin andyttrium in an amount effective to provide a coating comprising tin andyttrium in an amount of greater than or equal to about 0.05 atomicpercent based upon the total coating. The coating composition maypreferably also comprise a viscous binder if desired. After dipping thesubstrate 32 in the coating composition, the coated substrate may bepreferably heat treated at a temperature of at least about 1200° C., forat least about one hour, to form the environmentally resistant coating34. An additional heat treatment at temperatures up to about 1600° C.for a time period of up to about 10 hours may be used to consolidate theenvironmentally resistant coating 34.

When the substrate 32 comprises a Nb based RMIC composite, the coatingcomposition can be chosen to form the environmentally resistant coating34 with a minimum of reaction with the Nb based RMIC substrate 32 (sothat the formed coating 34 and the coating composition have a similarcomposition). Alternatively, the coating composition can be chosen toform the environmentally resistant coating 34 as a result of asubstantial reaction with the Nb based RMIC substrate 32 to effectivelydouble the coating 34 thickness, compared with the initial thickness ofthe applied coating composition. Thus, for example, a coatingcomposition comprising a combined amount of tin and yttrium greater thanor equal to about 0.1 atomic percent, may, after being applied to thesubstrate and subjected to heat treatment, form a crystalline coatinghaving a combined amount of tin and yttrium greater than or equal toabout 0.05 atomic percent.

When the substrate 32 comprising a molybdenum-silicide based composite,the coating composition is chosen to form the environmentally resistantcoating 34 with a minimum of reaction with the molybdenum-silicide basedcomposite. Thus as may be seen in FIG. 2, region 36 of the coating wouldremain molybdenum-free, while region 38 represents the region where thecoating adheres with molybdenum-silicide based composite and wherelittle or no reaction occurs.

Other methods, including ion plasma deposition, vacuum plasma spraying,high velocity oxy-flame spraying, physical vapor deposition, chemicalvapor deposition, and combinations comprising at least one of theforegoing methods, can be used to deposit the components such assilicon, chromium, titanium, and niobium on the substrate 32, preferablya Nb based RMIC substrate or the molybdenum-silicide based substrate.The environmentally resistant coating 34 may preferably be bonded to theNb based RMIC substrate or the molybdenum-silicide based substrate 32 byheating to a temperature of at least about 1200° C., for at least aboutone hour.

The environmentally resistant coating 34 that is formed on the Nb basedRMIC composite substrate 32 may further comprise several different anddistinct phases. The primary phase in the environmentally resistantcoating 34 is C14 Laves of the form (Nb,Ti)(Cr,Si,Al)₂, with about 30 toabout 37 atomic percent of niobium or combinations comprising niobiumand titanium, and about 63 to about 70 atomic percent of (Cr,Si,Al),where the specific ranges are about 28 to about 60 atomic percentchromium, up to about 35 atomic percent silicon, and up to about 42atomic percent of aluminum. Either aluminum or silicon is generallypresent in the C14 Laves phase.

In one embodiment, when the coating composition comprises about 5 toabout 55 atomic percent aluminum, the environmentally resistant coating34 may comprise a primary phase of the form (Nb,Ti,Cr)Al₃, with about 72to about 78 atomic percent aluminum and about 22 to about 28 atomicpercent (Nb,Ti,Cr), where the specific ranges are about 17 to about 28atomic percent of niobium or a combination of niobium or titanium and upto about 5 atomic percent chromium. In another embodiment, theenvironmentally resistant coating 34 may comprise several additionalprimary phases of the form (Cr,Nb,Ti)₅Si₃, with about 35 to about 39atomic percent silicon and about 61 about 65 atomic percent (Cr,Ti,Nb),where the specific ranges are about 40 to about 60 atomic percentchromium, up to about 5 atomic percent niobium and about 5 to about 25atomic percent Ti. In yet another embodiment, primary phases having thecomposition (Cr, Nb, Ti)₁₁Si₈, with about 39 to about 43 atomic percentsilicon, about 57 to about 61 atomic percent (Cr,Nb,Ti), having about 30to about 38 atomic percent chromium and about 20 to about 30 atomicpercent of either niobium or a combination of niobium and titanium.Another primary phase may be of the form (Cr,Ti,Nb)₆Si₅, with about 44to about 47 atomic percent silicon, and about 53 to about 56 atomicpercent (Cr,Nb,Ti), having about 25 to about 45 atomic percent chromiumand about 10 to about 30 atomic percent of niobium or a combination ofniobium and titanium.

Several other minor phases may also be present in the environmentallyresistant coating 34. These include CrSi₂, CrSi, and Cr₃Si, each ofwhich is narrowly stoichiometric, with an amount of less than or equalto about 5 atomic percent of niobium or a combination of niobium andtitanium. In general, the body centered cubic (bcc) portion of thechromium solid solution may be replaced with with niobium, titanium,silicon, or aluminum, while the bcc portion of the niobium solidsolution may be replaced with titanium, chromium, silicon, aluminum, theC15 Laves (Nb,Ti,Cr)₂Al, Nb₅Si₃ or Ti₅Si₃. In all of the phases, ironmay be used to partially replace chromium, and both chromium andgermanium (Ge) can partially replace silicon. The additions of yttriumand tin may be distributed in these phases, or may form separate phases,but their effects are not significant on the phase equilibria, butrather on the oxidation behavior.

These phases may also contain small amounts of chromium and hafnium, andmay be concentrated in the surface zone 36, rather than in aninterfacial zone 38 adjacent to the interface 39 between theenvironmentally resistant coating 34 and the molybdenum-silicide basedcomposite substrate 32 as can be seen in FIG. 2.

In general, the environmentally resistant coating 34 is a crystallinecoating and has a crystalline content greater than or equal to about 60weight percent (wt %), preferably greater than or equal to about 80 wt%, and most preferably greater than or equal to about 95 wt %, based onthe total weight of the coating composition. In general the thickness ofthe environmentally resistant coating 34 is about 10 to about 200micrometers. Within this range, a thickness of greater than or equal toabout 15 micrometers, preferably greater than or equal to about 20micrometers, and most preferably greater than or equal to about 25micrometers is desirable. Within this range, a thickness of less than orequal to about 175 micrometers, preferably less than or equal to about150 micrometers and most preferably less than or equal to about 125micrometers is desirable. As defined herein, the environmentallyresistant coating is one that will provide increased resistance tooxidation at temperatures of about 1090° C. to about 1370° C. and/orincreased resistance to pesting at temperatures of about 760° C. toabout 980° C.

In another embodiment, a thermal barrier coating 42 may be applied tothe environmentally resistant coating 34 to provide a thermal barriercoated article 50, such as a coated turbine component, as shown in FIG.3. The thermal barrier coating 42 is deposited on the outer surface 40of the environmentally resistant coating 34. The thermal barrier coating42 has a thickness of about 50 microns to about 400 microns, and maycomprise zirconia, zirconia stabilized by the addition of other metals,such as yttrium, magnesium, cerium, and the like, zircon and mullite,and other refractory materials having similar properties. Combinationsof the above materials may also be used. Once the thermal barriercoating 42 and environmentally resistant coating 34 have been applied toa turbine component, the thermal barrier coated turbine article 50 maybe installed in a turbine system.

The above-described methods of making turbine components and coatingthem with environmentally resistant coatings have a number of advantagesover other methods described in the prior art. The environmentallyresistant coatings protect the turbine components derived from Nb basedRMICs or molybdenum-silicide based composites from undergoing oxidationat higher temperatures of about 1090° C. to about 1370° C. In addition,they protect the turbine components from undergoing pesting at lowertemperatures of about 760° C. to about 980° C. The environmentallyresistant coatings are advantageous in that they display good adhesionto the thermal barrier coatings, which provide an additional layer ofprotection to the turbine components.

The following examples, which are meant to be exemplary, not limiting,illustrate compositions and methods of manufacturing some of the variousembodiments of the environmentally resistant coatings using variousmaterials and apparatus.

EXAMPLE 1

In this example, five alloy compositions (Samples 1-5 in Table 1) wereselected based upon a point near the end of the C14-Laves phase in theniobium-aluminum-chromium (Nb—Al—Cr) ternary system shown in FIG. 4.Samples 1-4 are comparative compositions. In addition, three alloycompositions (Samples 6-8 in Table 1) were studied based upon a point inthe two-phase region between the C14-Laves and Laves+NbAl₃ phases in theniobium-aluminum-chromium (Nb—Al—Cr) system as shown in FIG. 4. Of thesethree compositions, Samples 6 and 7 are comparative compositions. Allthe ingredients shown in Table 1 are measured in atomic percentages.

Ingots of each alloy composition having a 5 cm diameter×3.8 cm thicknesswere produced by vacuum arc melting. Pins of size 0.3 cm diameter×2.9 cmlong were then machined from each arc-cast ingot. The pins wereindependently oxidized in an open-air furnace for either 100 hours at871° C., 1204° C., and 1315° C. respectively, or for 10 hours at 1371°C. The furnaces provided a static air ambient atmosphere for theexposures. Following oxidation in the furnace, optical and scanningelectron microscopy (SEM) was performed on each of the oxidized pins todetermine the depth of penetration of the oxide layer into the material,and to observe microstructural characteristics and phase stabilitywithin each alloy. X-ray microanalysis was also performed at severalpoints within each alloy pin to determine the composition of pertinentphases and the oxide layer.

Oxidation penetration in the alloy pins was measured by two differentmethods. The first method consists of obtaining fifteen measurements ofoxide penetration around the perimeter of the pin. Average and standarddeviation values were calculated for each set of measurements obtained.The second method consists of subtracting the cross-sectional area ofeach pin determined ‘to be un-oxidized’ from the total cross-sectionalarea of each pin. The second measurement method more accurately takesinto account that some of the surface oxide formed on the pin may havebeen lost in the sample preparation steps. TABLE 1 Sample # NiobiumTitanium Aluminum Silicon Germanium Chromium Iron Tin Yttrium Tungsten1* 30 — 40 — — 30 — — — — 2* 20 — 40 20 20 — — — — 3* 20 — 40 10 10 20 —— — — 4* 10 10 40 10 10 20 — — — — 5  10  8 38 10  8 20 4 2 0.2 — 6*29.9 — 49 — — 20 — — 0.1 1 7* 15 15 49 — — 20 — — 0.2 — 8  14.8 12 45 —— 20 4 4 0.2 —*Comparative ExamplesAll the ingredients are in atomic percent.

The results for oxygen penetration obtained by the first method forSamples 1-8 are shown in Table 2 below, while the reduction in pindiameter obtained by the second method is shown in Table 3 below. Theresults for oxygen penetration and reduction in pin diameter made by thefirst and second methods are also depicted in FIGS. 5 and 6respectively. TABLE 2 871° C./ 1204° C./ 1315° C./ 1371° C./ 100 hr 100hr 100 hr 10 hr Sam- Mean Mean Mean Mean ple # (μm)** σ (μm)** σ (μm)**σ (μm)** Σ 1* 13.12 1.42 447.06 7.62 2079.09 17.36 — — 2* 9.30 7.1345.19 3.78 95.95 10.45 — — 3* 7.13 6.08 155.97 13.79 162.90 18.48 0.0045.62 4* 6.08 0.34 19.90 2.11 18.48 3.47 385.88 9.64 5  7.60 1.23 23.364.57 33.68 6.54 145.74 27.98 6* — 311.46 12.04 353.77 48.52 — — 7* 13.290.44 35.43 0.84 33.33 0.12 8.47 2.09 8  12.26 1.04 16.93 2.56 18.40 3.2024.71 2.48*Comparative Examples**Mean depth of oxide penetration in micrometers (μm)σ = standard deviation of oxide penetration in micrometers (μm)

TABLE 3 1204° C./ 1315° C./ 1371° C./ Sample # 871° C./100 hr** 100 hr**100 hr** 10 hr** 1* 26.24 532.61 2558.65 3048.00 2* 18.60 47.57 215.213048.00 3* 14.24 137.89 −223.09 830.94 4* 12.16 93.65 301.35 145.78 5 15.20 164.20 217.72 96.54 6* 3022.60 1069.64 2669.13 3048.00 7* 26.6086.55 172.78 108.40 8  24.60 162.14 577.70 178.11*Comparative Examples**Pin diameter reduction values in micrometers (μm)

FIGS. 5 and 6 are graphs showing the effect of alloy composition andexposure temperature on oxide penetration for Samples 1-5. FIG. 5, showsthat the alloy of Sample 2 obtained by addition of silicon to theC14-Laves phase dramatically improves oxidation resistance duringexposure at 871° C., 1204° C., and 1315° C. when compared with Sample 1.Further additions of germanium and titanium to Sample 2, create thealloy of Sample 4, which shows a better resistance to oxide penetrationthan Samples 1, 2 and 3. Similarly the addition of germanium, titanium,and iron along with a small amount of tin and yttrium to create Sample5, further provides improvements in oxidation resistance for thesealloys. For example, upon exposure at 1371° C. for 10 hours, the Samples1 and 2 quickly underwent oxidation and disintegrated into dust. On theother hand, Sample 5, which contained the germanium, titanium, and iron,tin and yttrium, showed improved oxidation resistance at 1371° C. overSamples 1-4 when retained at this temperature for a period of 10 hours.No significant oxidation or low temperature pesting was observed in anyof the samples exposed to 871° C. for a period of 100 hours.

FIG. 6 shows a plot wherein reduction in pin diameter (measured by thesecond method) due to oxidation is compared for the Samples 1-5 whensubjected to the aforementioned temperature conditions. The data plottedin FIG. 6 were calculated assuming that the pin was perfectlycylindrical before and after the pin was exposed to the high temperatureoxidation. In this figure it is clear that pins created from thecomposition of Sample 1, was drastically reduced in size by oxidationupon exposure at 1204° C., 1315° C. and 1371° C. FIG. 6, also shows thatSample 5 undergoes the least reduction in pin diameter when exposed totemperatures of 1371° C. for 10 hours.

Backscattered electron micrographs (taken in a scanning electronmicroscope) of Samples 2, 4, and 5 pins are shown in FIG. 7 afterexposure at 1315° C. for 100 hours. These micrographs reflect oxidationpenetration around the pin perimeter. The porosity in Samples 2 and 4 ismost likely due to the porosity in the case ingot. The pin made from thecomposition of Sample 4 may have been insufficiently homogenized duringingot making, as it apparently melted during oxidation. Sample 5 on theother hand reflects very little porosity indicating greater oxidationresistance.

FIG. 8 is a plot depicting oxidation penetration in Samples 6, 7 and 8as a function of exposure conditions and alloy composition. Once againSample 8, which contains tin and yttrium shows better resistance tooxidation penetration than Samples 6 at all temperatures and a betterresistance to oxide penetration at 1204° C. and 1315° C. than Sample 7.Sample 6 pins exposed at 871° C. for 100 hours or 1371° C. for 10 hoursdisintegrated to powders in the furnace due to extreme oxidation. FIG. 9shows micrographs of cross-sections of pins having the composition ofSamples 7 and 8. Micrographs of these alloy pins show minimal oxidepenetration around the perimeter of the sample. The excess porosity inSample 8 is most likely due to the porosity in the in cast ingot.

As shown in the above examples, the above-described methods of makingturbine components and coating them with the crystalline environmentallyresistant coatings have a number of advantages over other methodsdescribed in the prior art. Samples 5 and 8 advantageously provide asuperior resistance to oxide penetration at elevated temperatures ashigh as 1371° C. and can therefore protect the turbine componentsderived from Nb based RMICs or molybdenum-silicide based composites fromundergoing oxidation at temperatures of about 1090° C. to about 1370° C.In addition, they have proven that they can be capable of protecting theturbine components from undergoing pesting at lower temperatures ofabout 760° C. to about 980° C. The substrates with the environmentallyresistant coatings are further advantageous in that the substratesdisplay thermal expansion behavior very similar to the thermal barriercoatings. This similarity in thermal expansion behavior promotes reducedthermal expansion mismatching between the two layers thereby reducingthermal stresses, which provides additional protection to the turbinecomponents.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A turbine component comprising: a substrate; and a crystallinecoating disposed on a surface of the substrate, wherein the crystallinecoating comprises tin and yttrium in an amount greater than or equal toabout 0.05 atomic percent based upon the total coating.
 2. The turbinecomponent of claim 1, wherein the substrate is a niobium basedrefractory metal intermetallic composite comprising titanium, hafnium,silicon, chromium, and niobium or a molybdenum-silicide based compositecomprising molybdenum, silicon, and either boron, chromium or acombination of boron and chromium.
 3. The turbine component of claim 1,wherein the substrate is selected from the group consisting of rotatingblades, non-rotating vanes, shrouds, nozzles, and combustors.
 4. Theturbine component of claim 1, wherein the substrate is part of aircraftturbine system, a landcraft turbine system or a watercraft turbinesystem.
 5. The turbine component of claim 1, wherein the substratefurther comprises a thermal barrier coating disposed on a surface of thecrystalline coating on a side opposite the substrate.
 6. The turbinecomponent of claim 1, wherein the crystalline coating further compriseschromium and aluminum.
 7. The turbine component of claim 1, wherein thecrystalline coating further comprises about 25 to about 60 atomicpercent chromium, up to about 20 atomic percent aluminum, about 2 toabout 40 atomic percent niobium, about 5 to about 67 atomic percentsilicon, about 2 to about 40 atomic percent titanium, up to about 20atomic percent germanium, and up to about 10 atomic percent iron, basedupon the total coating.
 8. A turbine system comprising the turbinecomponent of claim
 1. 9. A method of making a turbine componentcomprising: disposing a coating composition on a substrate, wherein thecoating composition comprises tin and yttrium in an amount greater thanor equal to about 0.1 atomic percent based upon the total coatingcomposition.
 10. The method of claim 9, wherein the disposing comprises:applying to the substrate by dipping, painting, spray painting, orcombinations comprising at least one of the foregoing, a slurrycomprising tin and yttrium in an amount effective to provide a coatingcomprising tin and yttrium in an amount of greater than or equal toabout 0.05 atomic percent based upon the total coating; and heattreating the substrate for at least about one hour at a temperature ofat least about 1200° C.
 11. The method of claim 9, wherein the substrateis a niobium based refractory metal intermetallic composite comprisingtitanium, hafnium, silicon, chromium, and niobium or amolybdenum-silicide based composite comprising molybdenum, silicon, andeither boron or chromium.
 12. The method of claim 9, wherein thecrystalline coating further comprises chromium and aluminum.
 13. Themethod of claim 9, wherein the crystalline coating further comprisesabout 25 to about 60 atomic percent chromium, up to about 20 atomicpercent aluminum, about 2 to about 40 atomic percent niobium, about 5 toabout 67 atomic percent silicon, about 2 to about 40 atomic percenttitanium, up to about 20 atomic percent germanium, and up to about 10atomic percent iron, based upon the total coating.
 14. The method ofclaim 9, wherein the crystalline coating has a thickness of about 10microns to about 200 microns.
 15. The method of claim 9, wherein athermal barrier coating is further disposed on a surface of thecrystalline coating on a side opposite the substrate.
 16. A turbinesystem comprising the turbine component manufactured by the method ofclaim
 9. 17. A crystalline coating comprising tin and yttrium in anamount greater than or equal to about 0.05 atomic percent based upon thetotal coating.
 18. The crystalline coating of claim 17, furthercomprising chromium and aluminum.
 19. The crystalline coating of claim17, further comprising about 10 to about 67 atomic percent chromium,about 5 to about 55 atomic percent aluminum, and about 15 to about 45atomic percent of a combination of niobium and titanium, based upon thetotal coating.
 20. The crystalline coating of claim 17, furthercomprising up to about 15 atomic percent silicon, 15 to about 52 atomicpercent chromium, about 30 to about 50 atomic percent aluminum, about 10to about 25 atomic percent niobium, about 5 to about 20 atomic percenttitanium, up to about 15 atomic percent germanium, and up to about 8atomic percent iron, based upon the total coating.
 21. The crystallinecoating of claim 17, further comprising about 20 atomic percentchromium, about 37.9 atomic percent aluminum, about 10 atomic percentniobium, about 8 atomic percent titanium, about 10 atomic percentsilicon, about 8 atomic percent germanium, and about 4 atomic percentiron, based upon the total coating.
 22. The crystalline coating of claim17, comprising about 4 atomic percent tin, and about 0.2 atomic percentyttrium and further comprises about 20 atomic percent chromium, about 45atomic percent aluminum, about 14.8 atomic percent niobium, about 12atomic percent titanium, about 4 atomic percent iron, based upon thetotal coating.
 23. The crystalline coating of claim 17, comprising about25 to about 60 atomic percent chromium, up to about 20 atomic percentaluminum, about 2 to about 40 atomic percent niobium, about 5 to about67 atomic percent silicon, about 2 to about 40 atomic percent titanium,up to about 20 atomic percent germanium, and up to about 10 atomicpercent iron, based upon the total coating.
 24. The crystalline coatingof claim 17, comprising about 40 to about 60 atomic percent chromium, upto about 20 atomic percent aluminum, about 20 to about 25 atomic percentniobium, about 10 to about 20 atomic percent silicon, about 8 to about10 atomic percent titanium, and up to about 10 atomic percent iron,based upon the total coating.
 25. The crystalline coating of claim 17,comprising about 25 to about 40 atomic percent chromium, up to about 4atomic percent aluminum, about 5 to about 15 atomic percent niobium,about 49 to about 64 atomic percent silicon, about 5 to about 10 atomicpercent titanium, and up to about 4 atomic percent iron, based upon thetotal coating.
 26. The crystalline coating of claim 17, wherein thecoating has C14 Laves of the form (Nb,Ti)(Cr,Si,Al)₂, with about 30 toabout 37 atomic percent of niobium or combinations comprising niobiumand titanium, and about 63 to about 70 atomic percent of chromium,silicon and aluminum.
 27. The crystalline coating of claim 17, whereinthe coating comprises primary phases of the form (Nb,Ti,Cr)Al₃,(Nb,Ti,Cr)₂Al, Nb₅Si₃, Ti₅Si₃, (Cr,Nb,Ti)₅Si₃, (Cr, Nb, Ti)₁₁Si₈,(Cr,Ti,Nb)₆Si₅, CrSi₂, CrSi, Cr₃Si or combinations comprising at leastone of the foregoing phases.